In order to perform work in hot, hostile environments, workers are required to wear impermeable protective clothing together with supplied air respirators. It has been discovered that the use of such impermeable protective clothing inhibits the normal bodily cooling function which operates though the evaporation of body moisture. This results in heat stress which is the normal physiological response of the body to excessive heat load. Prolonged exposure to heat stress leads to heat illness such as heat rash, heat cramps, heat syncope (fainting), heat exhaustion and heat stroke. All of these are serious and heat stroke is life threatening. Not only is heat stress a serious health risk, it also reduces worker productivity and increases the frequency of errors as worker physical condition deteriorates.
One way of preventing heat stress when working in such hot, hostile environments is to reduce the length of time a worker is exposed to a heat stress inducing environment (stay time). However, the use of shorter stay times increases costs and prolongs the duration of some jobs requiring work in hot, hostile environments.
Medical studies have determined that providing breathing air at a reduced temperature results in sufficient body cooling to avoid heat stress for prolonged periods. In most applications providing breathing air at a temperature in the range of 50.degree.-65.degree. F. provides sufficient body cooling to permit workers to stay in a hot environment for six hours, a substantial improvement over uncooled air.
One system for providing cooled air employs a vortex tube cooler whose intake is connected to a source of respirable compressed air and whose cooled air output is connected to a manifold having fittings for connecting air hoses to multiple respirators. The amount of a cooling achieved by the vortex tube is controlled by manually controlling the exhaust valve on the hot air end of the vortex tube. This valve also controls the pressure in the manifold by varying the amount and temperature of cooled air flowing out through the cold air end of the vortex tube. Manifold pressure is also controlled by a manually operable manifold exhaust valve and must be maintained within a desired range to provide adequate air flow to respirator users. If air flow into the manifold is too high or too low, cooling performance is adversely affected. Cooling performance is also affected by inlet air pressure to the vortex tube. Excess cooling creates ice build up within the system. Whenever one or more respirator users connects or disconnects to the system or when ambient conditions vary or when intake air pressure or temperature varies, numerous manual adjustments must be made to the vortex tube exhaust valve, the manifold exhaust valve and the vortex tube intake valve in a time consuming iterative procedure to ensure optimum air cooling and air supply to the respirator users. This requires continual supervision by a trained operator as well as time consuming adjustments to reach a desired equilibrium condition. Further, the operator and cooling system must be located outside the containment of the hostile environment. This creates cooling capacity loss through the transmission line. Locating the operator inside the containment risks personnel exposure to the hostile environment.
Accordingly it is an object of the invention to provide an automatic self regulating air cooling system for respirator users.
It is a further object of this invention to provide such an automatic self regulating air cooling system which is compact, which is highly reliable, suitable for location within a hostile working environment and which has no requirement for electrical power.